There continues to be a growing demand for semiconductor power switching devices, i.e., devices capable of carrying large currents at high voltages. Such devices include bipolar and field effect transistors including, for example, the Insulated Gate Bipolar transistor (IGBT) and the Metal Oxide Semiconductor Field Effect Transistor (MOSFET). Notwithstanding significant advances in power device technologies, there remains a need for still higher-performing and more cost-efficient devices. For example, it is desirable to further increase current density relative to the total die area of a device. One of the limiting factors to higher current ratings is the breakdown voltage, particularly in the edge termination region. Because semiconductor junctions include curvatures, various techniques are employed to avoid otherwise high concentrations of electric field lines. It is conventional in power device design to incorporate edge termination structures along the outer periphery of the device in order to ensure that the breakdown voltage in this region of the device is not any lower than the active region of the device.
Three examples of conventional termination structures are shown in FIGS. 1A-1C. FIG. 1A shows a simplified cross-section view of a termination region with multiple floating P-type rings 108. P-type diffusion region 106 represents the last blocking diffusion of the active region. P-type floating rings 108 help achieve a higher breakdown voltage in the periphery region by spreading the electric fields in a uniform manner. In FIG. 1B, a planar field plate 112 is electrically tied to the last blocking diffusion region 106 of the active region, and thus is biased to the same potential. Similar to P-type rings 108 in FIG. 1A, field plate 112 improves the periphery breakdown voltage by uniformly spreading the fields. An even higher periphery breakdown voltage is obtained by combining the techniques in FIGS. 1A and 1B as shown in FIG. 1C. In FIG. 1C, floating P-type rings 108 are combined with planar field plates 112 to achieve an even more uniform spreading of the electric fields in the termination region.
However, diffusion rings and planar field plates occupy relatively large areas of the die and require additional masking and processing steps, thus resulting in increased cost. Accordingly, there is a need for cost-effective termination techniques whereby a high breakdown voltage is achieved with minimal or no increase in process complexity and minimal silicon area consumption.